F. Ridley — Igneous Rocks of the Warwickshire Coal-field. 563 



aggregates. There is also some calcite present, the rock effervescing 

 briskly when touched with acid. It is a diorite. 



Chilvers Coton Bailway-Cutting. A sheet three inches thick in 

 Lower Silurian Shales. 



A greenish-grey or greyish-green rock of very fine texture, pro- 

 fusely speckled with dark-green crystals and containing much 

 pyrites, crystallized in cubes. 



Under the microscope this rock appears to consist of pale green 

 serpentinous matter with interlacing sheaf-like aggregates of small 

 slender acicular crystals, having frequently rather ragged boundaries. 

 These crystals often undergo extinction at an angle of 19° from their 

 longest diameter, and it may be assumed from this and from their 

 pleochroism that they are hornblende. There appears to be very 

 little felspathic matter in this rock. There are, however, a few im- 

 perfectly formed crystals of labradorite present. The serpentine 

 may possibly be pseudomorphous after olivine, but the sections are 

 very irregular in form, and there is no positive evidence upon this 

 point. A few grains of augite are visible in this section, as well as 

 irregularly-shaped patches of pyrites. 



Chilvers Coton Eailway-Cutting. Intrusive in Lower Silurian 



Shales. 



A medium-grained crystalline rock of a pinkish-grey, closely 

 speckled with dull green crystals and containing minute specks of 

 pj'rites. 



Under the microscope it is seen to consist of triclinic felspar, 

 hornblende, rather sparsely distributed grains of magnetite and 

 pyrites, a very few minute crystals of apatite and some isotropic or 

 nearly isotropic matter, which may represent an interstitial glass. 

 The felspar appears as a rule to be labradorite. The rock is essen- 

 tially a diorite. 



Chilvers Coton Eailway-Cutting. Intrusive in Lower Silurian 

 Shales. Three feet from top of dyke. 



A greenish-grey crystalline rock of fine texture, containing 

 numerous minute specks of pyrites. 



The constituents of this rock appear under the microscope to be 

 triclinic felspar (labradorite), serpentine, apatite pyrites, and a little 

 unaltered augite. The serpentine, which is very plentiful in the 

 section, may be an alteration product after augite or after some other 

 mineral, but upon this point the section affords no trustworthy 

 evidence. The rock is probably some kind of andesite. 



Midland Quarry, Nuneaton Station. Intrusive in Hartshill Qnartzite. 



A very fine-grained purplish-grey rock showing under a pocket- 

 lens a small quantity of a light-green mineral resembling epidote 

 and minute octahedra of magnetite. The specimen attracts the 

 magnetic needle. 



Under the microscope the constituents are seen to be triclinic 

 felspar, augite, olivine, magnetite, and serpentine, the latter sub- 



